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Date:   Fri, 23 Oct 2020 12:21:30 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     David Runge <dave@sleepmap.de>, linux-rt-users@vger.kernel.org,
        Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Daniel Wagner <dwagner@suse.de>
Subject: Re: [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT
Message-ID: <20201023112130.GA23790@infradead.org>
References: <20201021175059.GA4989@hmbx>
 <20201023110400.bx3uzsb7xy5jtsea@linutronix.de>
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> -	if (!IS_ENABLED(CONFIG_SMP) ||
> +	if (!IS_ENABLED(CONFIG_SMP) || IS_ENABLED(CONFIG_PREEMPT_RT) ||
>  	    !test_bit(QUEUE_FLAG_SAME_COMP, &rq->q->queue_flags))

This needs a big fat comment explaining your rationale.  And probably
a separate if statement to make it obvious as well.